FIG. 7 shows one of procedures in a conventionally typically method of manufacturing a hollow blade. FIGS. 8 and 9 each show an essential part of a hollow blade 50 manufactured by the conventional method.
In the conventional method of manufacturing a hollow blade, a first blade body 51 with a recessed part 53 and a second blade body 52 formed so as to close the recessed part 53 are first put together. Then, the first and second blade bodies 51, 52 are joined by welding by means of a ultrasonic welding device thereby forming the hollow blade 50 internally provided with a hollow part 56 composed of a part of the recessed part 53.
In this case, the first blade body 51 is provided with a shelf surface 54 formed at an outer periphery of the recessed part 53. An outer peripheral part of the back face 52b of the second blade body 52 is laid on the shelf surface 54 of the first blade body 51 so that the second blade body 52 is faced with the first blade body 51 in a partly contact state. An outer peripheral end surface 51b between the shelf surface 54 and the surface 51a of the first blade body 51 is opposed to an outer peripheral end surface 52c of the second blade body 52 with a set space left, thereby creating a clearance 59 between both the outer peripheral end surfaces 51b, 52c.
In the state that the first and second blade bodies 51, 52 are faced with each other in a contact state, a horn 60 of the ultrasonic welding device is moved down from above the clearance 59. Thus, the end surface 60a of the horn 60 is located at a position of crossing the first and second blade bodies 51, 52 interposing the clearance 59 therebetween and comes into contact with both the blade bodies 51, 52 while pressing them. In this state, ultrasonic vibrations are applied to the blade bodies 51, 52 by the horn 60 in its pressing direction (direction of arrows a-b of FIG. 7).
Frictional heat resulting from the ultrasonic vibrations is produced between the shelf surface 54 of the first blade body 51 and the outer peripheral part of the back face 52b of the second blade body 52 which come into face-to-face contact with each other, and is also produced between each of the surfaces 51a, 52a of the first and second blade bodies 51, 52 and the end surface 60a of the horn 60 which come into face-to-face contact with each other.
If frictional heat produced due to contact between resin materials is compared with frictional heat produced due to contact between metal and resin, the former has a higher temperature. Accordingly, resin is more readily melted at a part where the back face 52b of the second blade body 52 is laid on the shelf surface 54 of the first blade body 51, so that a resin melting part 55 shown in FIG. 8 or a first resin melting part 55A shown in FIG. 9 is produced. The first and second blade bodies 51, 52 are joined to each other through the resin melting part 55 or the first resin melting part 55A.
On the other hand, on each of the surfaces 51a, 52a of the first and second blade bodies 51, 52, resin is softened through the application of pressure and ultrasonic vibrations by the horn 60 so that a circular impression 58 along the shape of the horn 60 is produced. As shown in FIG. 8, when the pressing force of the horn 60 is set smaller so as to reduce the depth of the impression 58 as small as possible, an amount of melting resin produced by the formation of the impression 58 is decreased. As a result, an amount of flow of the melting resin into the clearance 59 is also decreased so that the clearance 59 is substantially kept in its original state.
On the contrary, when the pressing force of the horn 60 is increased, the depth of the impression 58 becomes larger as shown in FIG. 9, so that the amount of meltingresin produced accompanying the formation of the impression 58 is increased. As a result, a part of the melting resin flows into the clearance 59 so that a second resin melting part 55B is formed at an upper portion of the clearance 59. The second resin melting part 55B joins the first and second blade bodies 51, 52 to each other.
The joint strength between the first and second blade bodies 51, 52 is mainly ensured by the resin melting part 55 (in the case of FIG. 8) or the first resin melting part 55A (in the case of FIG. 9). However, when both the blade bodies 51, 52 are also joined to each other through the second resin melting part 55B as shown in FIG. 9, the joint strength between both the blade bodies 51, 52 is increased, which is preferable in point of joint strength.
Problems to be Solved
Since the joint strength between the first and second blade bodies 51, 52 is mainly ensured by the resin melting part 55 (in the case of FIG. 8) or the first resin melting part 55A (in the case of FIG. 9) as mentioned above, the resin melting parts 55, 55A must be surely formed in order to ensure reliability on the manufacture of the hollow blade 50. In other words, it is necessary to check, in a quality inspection after the manufacture, that the parts in question have been subjected to welding by the ultrasonic welding device.
In this case, a particular need for mass production of the hollow blade 50 is that the quality inspection can be made with efficiency and reliability.
However, since the resin melting parts 55, 55A are located inside the hollow blade 50, the inspector cannot make a direct visual check of them from outside. Therefore, in order to perform the quality inspection of the hollow blade 50 with efficiency and reliability, it is necessary that a visual check of the resin melting parts 55, 55A can be made by the inspector even though it is in an indirect manner.
In the case of the hollow blade 50 manufactured by the conventional manufacturing method, the impression 58 can be an object of the visual check.
Next, a consideration will be given to the hollow blade 50 manufactured by the conventional manufacturing method shown in FIGS. 8 and 9.
In the hollow blade 50 shown in FIG. 8, the depth of the impression 58 produced on the surfaces 51a, 52a of the first and second blade bodies 51, 52 is reduced as small as possible. Accordingly, when the quality inspection is performed through a visual check of the impression 58, it is difficult to recognize the impression 58 and, in some cases, it may be difficult to judge whether a welding work has been made or not. Accordingly, the above-mentioned hollow blade 50 has a problem in point of efficiency and reliability of the quality inspection.
In the hollow blade 50 shown in FIG. 9, since the depth of the impression 58 is large, a visual check of the impression 58 can be made with ease and reliability, which makes the hollow blade 50 of this case seem preferable in point of efficiency and reliability of the quality inspection. Further, since the second resin melting part 55B is formed at the upper portion of the clearance 59, the hollow blade 50 of this case has an advantage in its increased joint strength.
However, when an impeller is formed of the hollow blades 50 with such an impression 58 having a large depth, it can be considered that large noise is produced at the position of the impression 58 in association with the rotation of the impeller, which is not preferable.
In addition, the formation of such an impression 58 having a large depth squeezes a part of melting resin out of the impression 58 in a radial direction, thereby forming a swelling 57 around the impression 58. Since the swelling 57 results in production of noise if it is left, it is required to be removed. This increases the number of manufacturing steps, which is an undesired effect.
The present invention has been made in view of the foregoing problems and therefore, has its object of providing a hollow blade on which an inspection for a joint work can be performed with efficiency and reliability through a visual check from outside while the smoothness of the blade surface is maintained and providing a method of manufacturing the hollow blade.